1. Field of the Invention
The present invention relates to a wired circuit board and, more particularly, to a wired circuit board suitably used for a suspension board with circuit.
2. Description of the Prior Art
For example, a suspension board with circuit used for a hard disk drive comprises a supporting board 1 made of stainless steel foil, a base layer 2 formed of an insulating material formed on the supporting board 1, a conductive layer 3 formed on the base layer 2 in the form of a specific circuit pattern, and a cover layer 4, formed of an insulating material, for covering the conductive layer 3, as shown in FIG. 11(d).
The suspension board with circuit, prevalent nowadays as the so-called Flying Lead, is formed to have terminals 5 formed on both sides of the conductive layer 3, rather than in only either side thereof, in order to meet the demand of recent years for electronic equipment to have increasingly higher density and reduced size.
Conventionally, the terminals 5 of the suspension board with circuit are formed on both sides of the conductive layer 3 in the following manner. First, the cover layer 4 is formed and simultaneously opened by use of a photo-resist and the like to form a first opening 7 for forming the terminal 5 in the cover layer 4 and expose a front side of the conductive layer 3, as shown in FIG. 11(a). Then, a second opening 8 for the terminal 5 to be formed in the supporting board 1 is formed in the supporting board 1 by a chemical etching and the like, as shown in FIG. 11(b). Sequentially, with the supporting board 1 as a mask, the base layer 2 exposed in the second opening 8 is opened by a plasma etching and the like, to form a third opening 9 for the terminal 5 to be formed in the base layer 2, so that a back side of the conductive layer 3 is exposed, as shown in FIG. 11(c). Thereafter, metal plated layers 6 are formed on both sides of the conductive layer 3 thus exposed, as shown in FIG. 11(d).
The metal plated layer 6 thus formed extends over the whole area of the conductive layer 3 exposed in the whole area of the third opening 9 in the base layer 2 formed by using the supporting board 1 as the mask, without leaving any space between the periphery of the metal plated layer 6 and the periphery of the third opening 9 in the base layer 2. As a result of this, the metal plated layer 6 formed in the second opening 8 also extends in the thickness direction thereof, without leaving any space between the periphery of the metal plated layer 6 and the periphery of the second opening 8 in the supporting board 1. Due to this, depending on thickness of the metal plated layer 6 formed, the metal plated layer 6 can contact the periphery of the opening 8 in the supporting board 1 to cause a short circuit from the contact between the metal plated layer 6 and the supporting board 1.
In practice, since the third opening 9 in the base layer 2 is formed with the second opening 8 of the supporting board 1 as the mask, the third opening 9 is sometimes made slightly larger than the second opening 8 in the supporting board 1, as shown in FIG. 11(d). This increases the risk of a short circuit being caused from contact between the metal plated layer 6 and the supporting board 1.
It is the object of the invention to provide a wired circuit board capable of surely preventing occurrence of a short circuit between a metal terminal layer and a metal supporting layer with a simple construction, to provide improvement in connection reliability and in voltage proof property.
The present invention is directed to a novel wired circuit board comprising an insulating layer formed on a metal supporting layer, a conductive layer formed on the insulating layer, a surface of the conductive layer being exposed by opening the metal supporting layer and the insulating layer, and a metal terminal layer formed on the conductive layer exposed in the openings of the metal supporting layer and the insulating layer, wherein a specified space is defined between a periphery of the metal terminal layer and a periphery of the opening of the metal supporting layer.
With this construction, since the specified space is defined between the periphery of the metal terminal layer and the periphery of the opening of the metal supporting layer, contact between the periphery of the metal terminal layer and the periphery of the opening of the metal supporting layer can be surely prevented. This can surely prevent occurrence of a short circuit caused from the contact therebetween, thus providing improved connection reliability and voltage proof property of the suspension board with circuit.
It is preferable that the conductive layer has a terminal forming portion for forming the metal terminal layer and the terminal forming portion is hollowed toward the metal supporting layer with respect to the remaining portions of the conductive layer.
With this construction, the distance from the front side of the metal supporting layer to the front side of the metal terminal layer is shortened to an extent corresponding to the hollowed portion from the remaining portion and, as a result of this, the metal terminal layer is placed closer to the outside of the metal supporting layer to that extent. This can produce the effect that for example when the connecting terminals of an external circuit are connected with the metal terminal layers in such a manner that those connecting terminals are laid over the metal terminal layers and are bonded to each other via supersonic vibration of a bonding tool, the pressure bonding can be well ensured, thus providing further improved connection reliability.
The wired circuit board of the present invention can be used as a suspension board with circuit.